#!/usr/bin/perl -w
# DNA.pm
# First package to manipulate DNA sequences
# (c) 2008/2/25 Natasha Khuri 

package DNA;   # give this package a name


sub count_base($$) {  # expect two scalar

  my ($base, $dna) = @_;
  my %hash = ();	
  while ( $char = chop($dna))
  {
	$hash{$char}++;
  }
  return $hash{$base};
}

# a complement is a string in which
# A is replaced with T, C is replaced with G
# T is replaced with A, G is replaced with C

sub complement($) { # expect a string
 
  my ($dna) = @_;
  my $complement = '';
  foreach ( split(//, $dna) )
  {
      $complement .= 'A' if $_ eq 'T';
      $complement .= 'T' if $_ eq 'A';
      $complement .= 'C' if $_ eq 'G';
      $complement .= 'G' if $_ eq 'C';
  }
  
  return $complement;
}

return 1; # satisfy require statement